I’m sure a large part of the problem is a general reluctance to be inconvenienced, especially in urban areas, but I’m also sure there are still enough American couples who would prefer to have a larger family, large enough to deal with the problem.
Several countries - Russia, Hungary - have recognized the problem and are putting policies in place to rectify it. But such policies are the last thing the US government, as currently constituted, would consider.
Many western European countries have tried to incentivize families, and all have failed. The commitments are simply too overwhelmingly for many young people who live for themselves alone.